Earth movers are employed to move relatively large volumes of earth. There are different types of these devices. There is a "push-pull" type device which has power driven front and rear wheels that move a blade across the ground and force dirt and soil into the bowl of the earth mover. Another type of earth mover is a scraper/elevator. This device is typically pulled from the front and has a scraper blade that contacts and lifts dirt. The dirt is then pushed to the rear of the bowl of the earth mover by the elevator which is a series of horizontal blades which are supported on either side by a driven chain. These rotating blades simply push the earth to the back of the bowl. When it is desirable to unload the earth mover, the floor of the bowl can be opened partially and a pusher forces the dirt forwardly. The blades in turn are reversed, if desired, and force the dirt out of the earth mover bowl.
Over a period of time the chains stretch and therefore the tension must be adjusted. In the past, the chains would ride on idler sprockets which were attached to a scissor-type linkage which could force the idler sprocket outwardly in turn adjusting the tension. This was a very difficult task usually requiring two people.